Process for obtaining pure alumina and alkali-metal carbonates



atented' Aug. 7, 1928.

UNITE STATES PATENT OFFICE.

TRITZ ROTHE, AACHEN, AND HANS BREIl'EK, F PORZ, NEAR COLOGNE, GERMANY,

ASSIGNOES TO THE FIRM RI-IENANIA. VEBEIIN' CHEMISCHER FABRIKEN A. (2%., OF

CULOG'NE, GERMANY,

PROCESS TUB OBTAINING PURE .hLlUMINA AND JiltIlhKllLl-METAL CARBONATE$.

.ll'o firawing'. Application filed tlctober 6, 119%, serial No. 60,92%, and in Germany Uctobcr 13, 19%.

lt is known that by heating substancescontaining alumina as for example bauxite,

with alkali-metal chlorides or sulphates, soda or potash and pure alumina can be obtained. t The processes in question have not, however, received industrial application. The reason for this is probably that the carrying out of the processes is very diflicult and necessitates a very complicated plant and that very considerable excesses of alumina are necessary tor the decomposition of the alkali-metal sulphate.

We have found that it is possible to convert the alumina in alumina-cont-aining'substances (bauxite, hydrogi llite, diaspore, clay. and others) almost quantitatively into aluminate by heating to incandescence with alkali-metal sulphates, if the heating of the mixture containing the said initial sub stances is carried out in a current of gas, as air, furnace gases or the like, in the presence of steam, using for this purpose temperatures of about 1100 C. or over.

e have also found that'by adopting the aforesaid measures it is unnecessary to employ alumina in the considerable excesses used in the known process in which up to 2.3 mols ot' Al tl are employed for every mol of na o. Tn the present case it is sufficient to use for very mol of A1 0 about 1 mol alkali-metal oxide in the form of'alkalimetal sulphateathis ratio being the same as that used in the known Le Chateliers process, in which alkali-metal oxide in the term of soda is employed. A

Tn the case of alumina minerals rich in silica there are added to the raw mixture consisting of alumina mineral and alkalimetal sulphate such"- quantities of calcium in the form of quicklime, calcium hydroxide, or salts ot calcium that 2 mols GaO go to every mol oi SiO tor the-purpose of converting the silicainto an insoluble compound.

The product obtained is a porous loose mass which may be easily 'comminuted and extracted with water. From the aluminate extract obtained the alumina can be obtained the known manner either by separation by means of carbon" dioxide or by churning i according to the Bayerproceefi-sodium carthe decomposition being passed into the furnace gases. can, however, be subjected in the form of The mixture of raw materials briquettes to the furnace gases in annular kilns in the presence of steam. In either case it is advantageous. to conduct the heat ing in an oxidizing mannerfi;

The following are examples oft-his process:

1. 100 parts of a French bauxite containing 55% ALO and 3% SiO, are intimately mixed with 82 parts of sodium sulphate and 5.5 parts of calcium carbonate (for corn bining with the silica) and heated to incandescence at 1180 C. in a revolving tube furnace heated with gas, steam being passed in at the same time. The sintered loose product obtained gives, in thecase of a total alumina content of 40.96%,,40.02% of A1 0 corresponding to a decomposition of approximately 98% of the-alumina employed.

2. 100 parts of the? same bauxite are briquetted with 5.5 parts of calcium carbonate and 105 partstof potassium sulphate,

heated electrically, in a muflie at 1150 G.

into which air and steam are passed.

The sinteredproduct shows a decomposi tion of 92% ot the alumina employed.

at we fclaim. and. desire to secure by Letters Patent of the United States is:--

l. The: process which consists in mixing minerals containingalumina with an alkalimetal sulphate and heating said mixture'to incandescenc'e in the presence of steam at a temperature of at least 1100-C. avoiding any reduction in the mixture during the process. v

2 T e p ce s. which wa is in runes o minerals containing alumina with an alkalimetal sulphate and heating said mixture to incandescence in an oxidizing atmosphere and in the presence of steam at a temperature of at least 1100 C.

3. The process which consists in'mixin minerals containing alumina and being ric in silica with an alkali-metal sulphate and lime in sufiicient proportionvto convert the silica in the alumina-containing minerals into calcium orthosllicate, and heatmg said mixture to incandescence in' the presence of steam at a temperature of at least 1100 C.

' avoiding any reduction in the mixture during the process. I

5. The process which consists in mixing minerals containing alumina and being rich in silica with such quantities of an alkalimetal sulphate that about 1 mol of the alkali-metal oxide is used to 1 mol of alumina and lime in suflicient roportion to convert the silica in the alumina-containing minerals into calcium orthosilicate, and heating said mixture to incandescence in the presence 6. The process which consists in mixing minerals containing alumina with an alkalimetal sulphate and heating said mixture in .the presence of steam in a revolving tube furnace at a temperature of at least 1100 C. avoiding any reduction during the process.

7. The process which consists in mixing minerals containing alumina with an alkalimetal sulphate, placing said mixture in the form of powder in a revolving tube furnace and heating it by suitable means, as furnace gases, to which 1s added the steam required for the reaction at a temperature of at least 1100 C. avoiding any reduction in the mixture during the process.

'8.'The process which consists in mixin bauxite with an alkali-metal sulphate and heating said mixture to incandcscence in the presence of steam at a temperature of at least 1100 C. avoiding any reduction in the mixture during the process.

' In testimony whereof we afiix our signatures.

DR. FRITZ ROTHE. DR. HANS BRENEK. 

